_Secondary qualities are measured by means of such effects as can be estimated in number or space._ (IV. 4.) LXX. _The Measure of Sounds, as high or low, is the_ Musical Scale, _or_ Harmonic Canon. (IV. 4.) LXXI. _The Measures of Pure Colours are the_ Prismatic Scale; _the same, including_ Fraunhofer's Lines; _and_ Newton's Scale _of Colours. The principal Scales of Impure Colours are_ Werner's Nomenclature _of Colours, and_ Merimée's Nomenclature _of Colours_. (IV. 4.) LXXII. _The Idea of_ Polarity _involves the conception of contrary properties in contrary directions:--the properties being, for example, attraction and repulsion, darkness and light, synthesis and analysis; and the contrary directions being those which are directly opposite, or, in some cases, those which are at right angles._ (V. 1.) LXXIII. (Doubtful.) _Coexistent polarities are fundamentally identical._ (V. 2.) LXXIV. _The Idea of Chemical_ Affinity, _as implied in Elementary Composition, involves peculiar conceptions. It is not properly expressed by assuming the qualities of bodies to_ resemble _those of the elements, or to depend on the_ figure _of the elements, or on their_ attractions. (VI. 1.) {19} LXXV. _Attractions take place between bodies, Affinities between the particles of a body. The former may be compared to the alliances of states, the latter to the ties of family._ (VI. 2.) LXXVI. _The governing principles of Chemical Affinity are, that it is_ elective; _that it is_ definite; _that it_ determines the properties _of the compound; and that_ analysis is possible. (VI. 2.) LXXVII. _We have an idea of_ Substance: _and an axiom involved in this Idea is, that_ the weight of a body is the sum of the weights of all its elements. (VI. 3.) LXXVIII. _Hence Imponderable Fluids are not to be admitted as chemical elements._ (VI. 4.) LXXIX. _The Doctrine of Atoms is admissible as a mode of expressing and calculating laws of nature; but is not proved by any fact, chemical or physical, as a philosophical truth._ (VI. 5.) LXXX. _We have an Idea of_ Symmetry; _and an axiom involved in this Idea is, that in a symmetrical natural body, if there be a tendency to modify any member in any manner, there is a tendency to modify all the corresponding members in the same manner._ (VII. 1.) LXXXI. _All hypotheses respecting the manner in which the elements of inorganic bodies are arranged in space, must be constructed with regard to the general facts of crystallization._ (VII. 3.) {20} LXXXII. _When we consider any object as_ One, _we give unity to it by an act of thought. The condition which determines what this unity shall include, and what it shall exclude, is this;--that assertions concerning the one thing shall be possible._ (VIII. 1.) LXXXIII.